The mechanism of wear of human enamel, composites, and polymer restorative and preventive materials, and dental amalgam under conditions of abrasive wear will be studied. The wear of these materials will be studied under conditions of single and multiple-pass sliding and the effects of load, velocity, environment, and wear debris on the wear mechanism will be determined. Wear tracks will be observed microscopically for evidence of the type of surface failure which should indicate the mechanism of wear for the various systems. This information should be useful in improving the wear resistance of dental materials.